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N. Ishikawa, Y. Fujimura, K. Kondo, G. Szabo, R. Wilhelm, H. Ogawa, T. Taguchi:
"Surface nanostructures on Nb-doped SrTiO₃ irradiated with swift heavy ions at grazing Incidence";
Nanotechnology, 33 (2022), 23530301 - 23530310.

A single crystal of SrTiO3 doped with 0.5 wt% niobium (Nb-STO) was irradiated with 200 MeV
Au32+ ions at grazing incidence to characterize the irradiation-induced hillock chains. Exactly
the same hillock chains are observed by using atomic force microscopy (AFM) and scanning
electron microscopy (SEM) to study the relation between irradiation-induced change of surface
topography and corresponding material property changes. As expected, multiple hillocks as high
as 5-6 nm are imaged by AFM observation in tapping mode. It is also found that the regions in
between the adjacent hillocks are not depressed, and in many cases they are slightly elevated.
Line-like contrasts along the ion paths are found in both AFM phase images and SEM images,
indicating the formation of continuous ion tracks in addition to multiple hillocks. Validity of
preexisting models for explaining the hillock chain formation is discussed based on the present
results. In order to obtain new insights related to the ion track formation, cross-sectional
transmission electron microscopy (TEM) observation was performed. The ion tracks in the nearsurface
region are found to be relatively large, whereas buried ion tracks in the deeper region are
relatively small. The results suggest that recrystallization plays an important role in the formation
of small ion tracks in the deep region, whereas formation of large ion tracks in the near-surface
region is likely due to the absence of recrystallization. TEM images also show shape deformation
of ion tracks in the near-surface region, suggesting that material transport towards the surface is
the reason for the absence of recrystallization.

swift heavy ion, hillocks, ion-tracks, ion irradiation, TEM, AFM, SEM

http://dx.doi.org/10.1088/1361-6528/ac58a5

https://publik.tuwien.ac.at/files/publik_303721.pdf